With the problem of population aging, an increasing number of people are suffering from senile dementia (such as those associated with Alzheimer's disease, vascular dementia, Parkinson's disease, Lewy body disease, etc). They have the history of gone missing or eloping from their homes. General speaking, these patients usually do not have any immediate danger, but oftentimes their families do not have any idea of their whereabout and become very anxious. Apart from a few unfortunate cases, most of these patients could be located after some time. But It takes a great deal of effort and resources to locate these patients in a reasonable time frame. In the process, their families and friends may endure a great deal of stress.
In principle, locating technologies known in the art, e.g., Global Positioning System (GPS) could be used to help locating the missing persons. GPS receivers can give a precise location fixed in a range of 10 meters if the patient is in an outdoor location where satellite signals can be easily received. However, satellite signals can be difficult, if not impossible, to receive in the over-populated metropolitan areas, such as Hong Kong, Tokyo, etc, because of the surrounding tall and dense buildings. The situation is even worse if the patient is staying indoors. Therefore there is a need for a tracking system to locate a person suffering from senile dementia within a room inside a building in an over populated city such as Hong Kong, where there are many hundreds of tall buildings and a typical building has 20 to 60 floors and each floor has 4 to 50 rooms.